The emission spectrum of a light emitting diode (“LED”) typically exhibits a single rather narrow peak at a wavelength (“peak wavelength”) determined by the structure of the light emitting diode and the composition of the materials from which it is constructed. For example, the emission spectra of InGaN based LEDs typically peak at wavelengths from about 400 nanometers (nm) to about 450 nm (UV to blue) and typically have widths at half maximum of about 20 nm to about 50 nm.
Luminescent materials (“phosphors”) are used with LEDs to produce light emitting devices with different wavelengths. The light emitted by the LED is absorbed by the phosphors, and the phosphors emit light of a different wavelength in response to the absorbed light. For example, InGaN based LEDs can be used with phosphors to produce green light with wavelengths of about 536 nm. A portion of the blue light emitted by the InGaN based LED is absorbed by the phosphors, which in response emit green light.
Phosphor converted LEDs are useful for producing light of different wavelengths, but the phosphors may contain or produce contaminants that degrade the performance of a LED. Contaminants may migrate to and react with a layer of the LED, thereby degrading the performance of the LED. Contaminants may also be present in materials used in packaging LEDs, such as encapsulation materials. Moisture is another source of contamination of LEDs.
Thus, there is a need to reduce the likelihood of contamination of light emitting diodes.